Question

How to balance the chemical equation Na+O2 --------- Na2O

Answer 1

Balanced equation=2 Na2 + O2 = 2 Na2O

Answer 2

The balancing of a ‘chemical equation’ involves the balancing of all atoms at both sides of the chemical equation. It means the ‘number of atoms’ must be same at ‘both sides’ of the chemical equation.

Hence here also to balance the equation we need to check the ‘number of atoms’ at both sides of the chemical equation.  Here one Na must be balanced by two Na atoms at both sides.  

$\bold{2 \mathrm{Na}+\mathrm{O}_{2} \rightarrow \mathrm{Na}_{2} \mathrm{O}}$